1. Field of the Invention
The invention concerns compositions and processes for bleaching substrates directly with air.
2. The Related Art
Oxygen bleaches are well known for their ability to remove stains from substrates. Traditionally the substrate is subjected to hydrogen peroxide or substances which can generate hydroperoxyl radicals. The latter may be inorganic or organic peroxides. Generally these systems must be activated. A method of activation is to employ wash temperatures of 60.degree. C. or higher. Unfortunately, these high temperatures often lead to inefficient cleaning. They can also cause premature damage to the substrate.
A preferred approach to generating hydroperoxyl bleach radicals is the use of inorganic peroxides coupled with organic precursor compounds. These systems are employed for many commercial laundry powders. European systems are based on tetraacetyl ethylenediamine (TAED) as the organic precursor coupled with sodium perborate or sodium percarbonate. Well known in the United States are laundry bleach products based on sodium nanonyloxybenzenesulphonate (SNOBS) as the organic precursor coupled with sodium perborate. Precursor systems are generally effective yet they still exhibit several disadvantages. For example, organic precursors are moderately sophisticated molecules requiring multi-step manufacturing processes resulting in high capital costs. Secondly, precursor systems have large formulation space requirements; a significant percent of a laundry powder must be devoted to the bleach components leaving less room for other active ingredients and complicating development of concentrated powders. Moreover, precursor systems do not bleach very efficiently in countries where consumers have wash habits entailing low dosage, short wash times, cold temperatures and low wash liquor to cloth ratios.
A long cherished dream has been to use air directly as the oxygen source. Air would avoid costly synthesized organic precursors. Unfortunately, air is kinetically inert towards bleaching substrates due to the spin barrier restriction and exhibits no bleaching ability. Recently some progress has been made in this area.
WO 97/38074 reports use of molecular oxygen (air) for oxidizing stain from fabrics. It was discovered that fabrics can be bleached by bubbling air through an aqueous solution containing an aldehyde. A broad range of aliphatic, aromatic and heterocyclic aldehydes were reported to be useful, particularly para-substituted aldehydes such as 4-methyl-, 4-ethyl- and 4-isopropyl benzaldehyde. It was also necessary in these systems to employ a radical initiator. A broad range of initiators were disclosed including N-hydroxysuccinimide, various peroxides and transition metal coordination complexes. While this disclosure appears to be a step-change in bleach chemistry, it is clear that more work is required to reveal the optimum system.
Accordingly, it is an object of the present invention to provide an optimum bleaching system with improved stain removal efficacy based on air or molecular oxygen.
Another object of the present invention is to provide a bleaching system which is cost-effective and environmentally friendly.
Still another object of the present invention is to provide a bleaching system based on air that is operable under harsh wash conditions which includes low temperatures, short contact times and low dosage requirements.
Yet another object of the present invention is to provide an improved hygiene or antimicrobial benefit coupled with a reduction in dye transfer damage.
These and other objects of the present invention will become more readily apparent from the following summary and detailed description.